Preheat the oven to 450°F.
In a medium bowl, combine the ground chicken, pickle juice, garlic powder, onion powder, dried dill, paprika, salt, pepper, and parmesan, if using. Mix gently with your hands until evenly combined — don't overwork it.
Lay a large piece of parchment paper on a flat surface or cutting board. Dust generously with cassava flour. Add the chicken mixture to the center. Dust the top with a little more cassava flour, then lay a second piece of parchment on top. Press and flatten into one large oval or rectangle, about ¼ inch thick — roughly the size of a standard sheet pan. Thinner and more even = crispier crust. Remove the top parchment. In a shallow bowl or plate, mix the GF panko with the fine sea salt, garlic powder, and black pepper until evenly combined.
Brush the top surface of the cutlet generously with egg wash. Press half the seasoned panko evenly over the top and press gently to adhere. Spray generously with avocado oil spray.
Place a baking sheet directly on top of the breaded cutlet. With one hand on the parchment underneath and one on the baking sheet, flip confidently in one decisive motion. Peel away the parchment now on top.
Brush this side with egg wash, press on the remaining seasoned panko, and spray again generously with avocado oil.
Transfer to the oven and bake at 450°F for 18–22 minutes, until deeply golden and crispy all over and the internal temperature reaches 165°F. Check about half way through and remove pan from oven to spray with more oil if it looks dry.
Broil for 1–2 minutes at the end for extra crunch (watch closely!).